The present invention relates to a temperature adjustment apparatus, and more particularly to a temperature adjustment apparatus equipped with a circulation path that passes through a subjected member wherein medium is passed through the circulation path to thereby conduct temperature setting.
Conventionally, a method using a plasma apparatus is known for etching dielectric films (SiO2) or the like formed on the surfaces of semiconductor wafers.
In such a plasma apparatus, a pair of electrodes is provided in a chamber that is capable of reducing pressure therein. A high-frequency plasma generation apparatus is connected to one of the electrodes and a grounding potential is connected to the other electrode such that plasma can be generated between the electrodes. Gas to be used for etching is introduced into the chamber and at the same time plasma is generated between the electrodes to perform an etching on semiconductor wafers that have been disposed in advance between the electrodes.
It is noted that, in etching semiconductor wafers using a plasma apparatus, temperature control for the electrodes is an important factor in order to stabilize the etching. Therefore, in general, the electrodes are provided with a temperature adjustment apparatus in an attempt to keep the temperature of the electrodes constant. The temperature adjustment apparatus is composed of a container for containing a medium with a temperature adjustment system and a circular path that is led out from the container and passes through the electrodes. The medium whose temperature is adjusted to a specified level in the container is sent to the electrodes, to thereby set the temperature of the electrodes at a specified level. If a medium having a low insulation resistance value is used, the dielectric constant between the electrodes may vary. Therefore PFC in a liquid state having a large insulation resistance value is normally used as the medium. (Pure water has a large insulation resistance value in an initial state, but its resistance value lowers when metal dissolves in the pure water while being circulated.)
In the temperature adjustment apparatus described above, the container that contains the PFC is not a sealed type, but has a structure in which the liquid surface of the PFC is exposed to the atmosphere. As a result, in the apparatus, the PFC evaporates into the atmosphere, and therefore the PFC needs to be periodically supplemented. Furthermore, since the PFC has a high GWP (global warming potential) that is several ten thousands times higher than that of carbon dioxide, it is not environmentally preferable to be discharged into the atmosphere. For example, when 0.015 m3 (15 litters) of PFC composed of C4F20 (its specific gravity being 1.8) is contained in the container, and the operation is conducted at 40xc2x0 for two weeks, it has been confirmed that 10 Kg of the PFC evaporates.
A sealed type container may be used for containing PFC to prevent evaporation of the PFC as a countermeasure. However, the container has to have a structure that sustains pressure variations, and therefore this is not generally practiced.
Also, when a medium other than PFC is used in an apparatus other than a plasma apparatus, the medium needs to be frequently supplemented, and therefore monitoring the quantity of the medium and supplementing the medium require substantial maintenance.
The present invention has been made in view of the problems of the conventional art, and it is an object of the present invention to provide a temperature adjustment apparatus that can reduce evaporation of a medium without using a sealed type container.
The present invention has been made based on the discovery that, when the area of a medium that is in contact with the atmosphere is reduced or a liquid cap is provided between a medium and the atmosphere, evaporation of the medium into the atmosphere can be reduced.
Accordingly, a temperature adjustment apparatus is characterized in comprising: a container that contains a medium for heat exchange and adjusts the temperature of the medium, and a circulation path for the medium that is led out from the container and passes through a subjected member, wherein a liquid layer that separates from the medium is formed over the medium contained in the container to prevent evaporation of the medium into the atmosphere. A liquid cap is present in an upper layer over the medium contained in the container, such that the medium does not directly contact the atmosphere. Accordingly, the rate at which the medium evaporates through the liquid layer into the atmosphere can be reduced. Also, the container does not need to be in a sealed type to prevent evaporation of the medium, such that the need to make the container to sustain pressure variations is eliminated.
A temperature adjustment apparatus can also be is characterized in that a restricted section is provided in an upper portion of the container such that a liquid surface level of the liquid layer is located in the restricted section. The opening area is reduced by the provision of the restricted section in the container such that an area of the medium contacting the atmosphere through the liquid layer can be reduced. As a result, evaporation of the medium into the atmosphere through the liquid layer can be further reduced.
A temperature adjustment apparatus can further be characterized in comprising: a container that contains a medium for heat exchange and adjusts the temperature of the medium, and a circulation path for the medium that is led out from the container and passes through a subjected member, wherein a restricted section is provided in an upper portion of the container such that a liquid surface level of the medium is located in the restricted section. The opening area is reduced by the provision of the restricted section in the container such that an area of the medium contacting the atmosphere can be reduced. As a result, evaporation of the medium into the atmosphere can be further reduced.
A temperature adjustment apparatus can also be characterized in comprising: a container that contains a PFC for heat exchange and adjusts the temperature of the PFC, and a circulation path for the PFC that is led out from the container and passes through a pair of electrodes of a plasma processing apparatus that generates plasma between the pair of electrodes, wherein a liquid layer that separates from the PFC is formed over the PFC contained in the container to prevent evaporation of the PFC into the atmosphere. The temperature control for the electrodes in the plasma apparatus is conducted by using PFC (perfluorocarbon and compounds thereof (HFC) in which part of PFC is replaced with hydrogen). When PFC is used as a medium, the dielectric constant between the electrodes in the plasma apparatus does not change because the insulation resistance value of the PFC is large. As a result, the characteristic of plasma generated between the electrodes can be maintained constant. Furthermore, since a liquid layer is provided in an upper layer of the PEG contained in the container, and the liquid layer is used as a liquid cap, the PEG does not contact the atmosphere. As a result, the PEG is evaporated into the atmosphere through the liquid layer such that the evaporation of the PFC into the atmosphere can be further reduced. Also, the container does not need to be in a sealed type to prevent evaporation of the PFC, such that the need to make the container to sustain pressure variations is eliminated.
A temperature adjustment apparatus can further be characterized in that a restricted section is provided in an upper portion of the container such that a liquid surface level of the liquid layer is located in the restricted section. The opening area is reduced by the provision of the restricted section in the container such that an area of the PFC contacting the atmosphere through the liquid layer can be reduced. As a result, evaporation of the PFC into the atmosphere through the liquid layer can be further reduced.
A temperature adjustment apparatus can also be characterized in that the liquid layer is formed from water. Water separates from PFC, and is readily available. Therefore, water can be readily used as the liquid layer and achieve the prevention of evaporation of the PFC.
A temperature adjustment apparatus can further be characterized in comprising: a container that contains a PFC for heat exchange and adjusts the temperature of the PFC, and a circulation path for the PFC that is led out from the container and passes through a pair of electrodes of a plasma processing apparatus that generates plasma between the pair of electrodes, wherein a restricted section is provided in an upper portion of the container such that a liquid surface level of the PFC is located in the restricted section.
The temperature control for the electrodes in the plasma apparatus is conducted by using PFC (perfluorocarbon and compounds thereof (HFC) in which part of PFC is replaced with hydrogen). When PFC is used as a medium, the dielectric constant between the electrodes in the plasma apparatus does not change because the insulation resistance value of the PFC is large. As a result, the characteristic of plasma generated between the electrodes can be maintained constant. Furthermore, the opening area is reduced by the provision of the restricted section in the container such that an area of the PFC contacting the atmosphere can be reduced. As a result, evaporation of the PFC into the atmosphere can be reduced.